Image sensors are made of an array of pixels. Within each pixel, some regions are specifically designed to be photosensitive, and other regions are protected from light by a lightshield. Regions are protected from light because light absorbed in these protected regions causes degraded performance through mechanisms such as color crosstalk, smear, or reduced blooming control.
In U.S. Pat. No. 6,867,062 by Eric G. Stevens, a thin lightshield process is described for providing a lightshield from one of the layers of a bi-layer metallization process. The aluminum layer in this process is usually patterned with a chlorine-based plasma chemistry which leaves chlorine-containing residue on the wafers after the etch. Further, this residue may react with the aluminum or TiW, especially where the aluminum and TiW meet, causing corrosion of these films, and degradation of their electrical properties or optical light-shielding properties. In addition, U.S. Pat. No. 6,867,062 requires that the etch of the bottom layer of the bi-layer metal be masked in some regions by the top layer of the bi-layer metallization. This requirement may restrict the use of certain metals for the bi-layer metallization.
Consequently, a need exists for producing image sensors that overcome the above-described drawbacks.